Animal Core will serve all of the proposed projects in this application. It will provide continued selective breeding and behavioral characterization of two lines of rats that have been bred for 8 generations on the basis of differences in novelty-seeking. This trait is related to differential responsiveness to drug abuse and to differences in other behavioral and neural characteristics. The Core will conduct the animal husbandry, the testing needed for continued breeding of the colony, the initial behavioral characterization (e.g. locomotor tests) of the animals prior to transferring them to the individual investigators for specific studies. Moreover, the Animal Core will maintain the two mouse lines necessary for Project 4, with either constitutive or inducible GR over-expression. It will conduct the genotyping necessary for identifying the transgenic animals and wild type littermates prior to their use for the proposed specific studies.